JP2011003468A - Superconductive cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a superconductive cable capable of reducing loss of an alternating current.SOLUTION: The superconductive cable is provided with a cable core which has a superconductive conductor layer formed by spirally winding a plurality of superconductive wire rods 120 on the outer circumference of a former 11, and the superconductor layer has a multi-layer structure in which the superconductive wire rod 120 is laminated in radial direction of the cable core. Then, in the superconductive conductor layer, an outer circumference side layer is formed by winding spirally the superconductive wire rod 120 similarly on the outer circumference of the inner circumference side layer 12a, and a magnetic field smoothing layer 12m consisting of a magnetic material is installed between the inner circumference side layer and the outer circumference side layer.

Description

  The present invention relates to a superconducting cable having a superconducting conductor layer having a multilayer structure. In particular, the present invention relates to a superconducting cable that can reduce AC loss.

  A superconducting cable is expected as an energy saving technology because it has a compact shape and can transmit a large amount of power as compared with a conventional power cable. Recently, research and development of a cable structure with lower loss as well as higher performance of the superconducting wire itself have been actively promoted (see, for example, Patent Document 1).

A superconducting cable cools a superconducting conductor layer by storing a cable core having a superconducting conductor layer in a heat insulating pipe having a double pipe structure and circulating a refrigerant (eg, liquid nitrogen (LN ₂ )) in the heat insulating pipe. A typical structure is a superconducting state.

  FIG. 3 is a diagram showing a typical basic structure of a superconducting cable. The superconducting cable 100 has a structure in which three cable cores 10 are twisted and housed together in a heat insulating tube 20. The heat insulating tube 20 is a corrugated tube having a double tube structure including an inner tube 21 and an outer tube 22, and a heat insulating material 23 is disposed between both the tubes 21 and 22. An anticorrosion layer 24 is formed on the outer periphery of the heat insulating tube 20 (outer tube 22).

  On the other hand, the cable core 10 has a structure in which a former 11, a superconducting conductor layer 12, an insulating layer 13, a superconducting shield layer 14, and a normal conducting protective layer 15 are arranged in order from the center. The former 11 generally has a circular outer shape, and is generally formed by twisting a plurality of copper strands coated with an insulating coating. The superconducting conductor layer 12 is formed by spirally winding a plurality of tape-shaped superconducting wires 120 around the outer periphery of the former, and has a multilayer structure in which the superconducting wires 120 are laminated in the radial direction of the cable core as shown in the figure. . Also, in the superconducting conductor layer 12, between the superconducting wires constituting each layer (between the inner peripheral layer 12a and the outer peripheral layer 12b in FIG. 4B), an interlayer paper such as kraft paper is used. An interlayer insulating layer (indicated by reference numeral 12i in FIG. 4B) is formed and is electrically insulated. The size of the interlayer paper is about 20 mm wide and about 50-100 μm thick.

As superconducting wires, Bi (bismuth) -based silver sheath wires and RE123-based thin film wires are known (RE: rare earth elements such as Y (yttrium), Ho (holmium), Nd (neodymium), Sm (samarium), Gd (Gadolinium). Bi-based silver sheath wire is a superconductivity represented by Bi ₂ Sr ₂ CaCu ₂ O _x (Bi2212) or (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + d} (Bi2223) in a silver or silver alloy sheath. It is manufactured by filling body powder and drawing, sintering, and rolling. On the other hand, RE123-based thin film wire deposits a superconductor thin film represented by, for example, REBa ₂ Cu ₃ O _7-d (RE123) on a substrate such as stainless steel or Ni-based alloy (eg, Hastelloy (registered trademark)). It is manufactured by. In particular, it is said that a thin film wire is generally superior in loss characteristics with respect to a parallel magnetic field than a silver sheath wire because the thickness of the superconducting thin film is thin.

  For example, Patent Document 2 discloses a power cable in which a double magnetic shield is disposed around a superconducting wire.

Japanese Patent Laid-Open No. 2005-100777 JP 58-147906 A

  However, conventional superconducting cables are insufficient in reducing AC loss, and further improvements are desired.

  In consideration of the bending characteristics of the cable core, the superconducting conductor layer is provided with a gap g between adjacent superconducting wires 120 as shown in FIG. In addition, a silver sheath or a substrate is used for the superconducting wire in consideration of workability, mechanical strength, and handleability. When the superconducting wire is spirally wound around the former, the wire is difficult to bend and deform along the former. As shown in FIG. 4A, when the former 11 around which the wire 120 is wound is viewed in cross section, the wire 120 The outer shape (contour) drawn by becomes a polygon.

  In such a superconducting cable, when an alternating current flows through the superconducting wire, an alternating magnetic field is generated along the circumferential direction in each of the superconducting conductor layers formed by the wire. The magnetic field in the circumferential direction at this time depends on the outer shape drawn by the wire, and is not a circle but a polygon. A radial magnetic field is generated. In particular, since the gap is provided at this location, the magnetic field is greatly disturbed. As a result, in the conventional cable core structure illustrated in FIG. 4B, the radial magnetic field generated due to the current flowing in the wire 120 constituting the inner peripheral layer 12a is generated between the wires. Leakage occurs from the provided gap, and since the voltage is applied perpendicularly to the tape surface of the wire 120 constituting the outer peripheral layer 12b, a large AC loss occurs in the outer peripheral layer.

  The present invention has been made in view of the above circumstances, and one of its purposes is to provide a superconducting cable capable of reducing AC loss.

  In order to reduce the AC loss generated in the outer peripheral layer, the circumferential magnetic field in the inner peripheral layer may be smoothed so as to approach a circle. Therefore, it is conceivable to make the wire more thin as one means for bringing the outer shape drawn by the wire closer to a circle. However, the thinning of the wire rod requires a lot of time for the winding work due to a decrease in winding workability accompanying an increase in the number of wires used. Moreover, management of the gap between adjacent wires becomes difficult due to an increase in the number of wires used.

  The superconducting cable of the present invention includes a cable core having a superconducting conductor layer formed by spirally winding a plurality of superconducting wires around the outer periphery of the former, and the superconducting conductor layer is formed by stacking superconducting wires in the radial direction of the cable core. It has a multilayer structure. In the superconducting conductor layer, a magnetic field smoothing layer made of a magnetic material is provided between the inner peripheral layer and the outer peripheral layer.

  According to this configuration, the magnetic field smoothing layer made of a magnetic material is applied to the outer peripheral layer by smoothing the magnetic field generated by the inner peripheral layer so as to approach a circle along the circumferential direction. Since the radial magnetic field decreases, AC loss can be reduced.

  The magnetic material constituting the magnetic field smoothing layer preferably has a high relative permeability. For example, the relative permeability is preferably 10 or more, particularly 20 or more. A magnetic material having a high relative permeability is easy to pass a magnetic field and contributes to the smoothing of the magnetic field.

  More preferably, the relative permeability of the magnetic material should be higher than the relative permeability of any material constituting the superconducting wire. This is because when the relative magnetic permeability of the magnetic material constituting the magnetic field smoothing layer is lower than the relative magnetic permeability of the material constituting the superconducting wire, the radial magnetic field generated in the inner peripheral layer is applied to the magnetic field smoothing layer. Compared to the superconducting wire constituting the outer layer, the AC loss reduction effect may be insufficient. On the other hand, when the relative permeability of the magnetic field smoothing layer is higher than the relative permeability of the superconducting wire, it is easy to obtain an AC loss reduction effect.

  As described above, the magnetic material preferably has a high magnetic permeability, but more preferably a soft magnetic material having a high magnetic permeability and a low hysteresis loss. If the hysteresis loss is low, the hysteresis loss generated by the magnetic field applied to the magnetic field smoothing layer can be reduced, and thus reduction of the AC loss can be expected. Specific examples of soft magnetic materials include pure iron, nickel, cobalt, silicon steel, permalloy, and ferrite.

  The thickness of the magnetic field smoothing layer is preferably 0.5 μm or more and 2 μm or less. As the magnetic field smoothing layer becomes thicker, the hysteresis loss tends to increase accordingly. Therefore, by setting the thickness of the magnetic field smoothing layer to 0.5 μm or more, it is possible to suppress hysteresis loss by setting the thickness to 2 μm or less while ensuring a magnetic path.

  The superconducting wire is preferably a thin film wire. As described above, the thin film wire is superior in the loss characteristics with respect to the parallel magnetic field as compared with the silver sheath wire, and it is expected that the effect of reducing the AC loss according to the present invention is increased. Further, by using a thin film wire, it is possible to reduce the thickness of the superconducting conductor layer, and to reduce the diameter of the cable core and thus the entire superconducting cable.

  In the superconducting cable of the present invention, a magnetic field smoothing layer is provided between the inner peripheral layer and the outer peripheral layer in the superconducting conductor layer having a multilayer structure, so that AC loss can be reduced.

It is a principal part schematic sectional drawing of the superconducting conductor layer of the cable core in the superconducting cable which concerns on Embodiment 1, (A) shows the case where the cross-sectional shape of a magnetic field smoothing layer is formed along the external shape which a wire draws, (B) shows the case where the cross-sectional shape of the magnetic field smoothing layer is formed in a circular shape. It is a schematic perspective view of a magnetic tape, (A) shows the magnetic tape which consists only of magnetic materials, (B) shows the magnetic tape which coat | covered the magnetic material on the base-material surface. It is a schematic perspective view explaining the typical basic structure of a superconducting cable. (A) is a schematic sectional drawing explaining the state which wound the superconducting wire around the former. (B) is a partially enlarged schematic sectional view for explaining a superconducting conductor layer formed by winding a superconducting wire.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Moreover, the same code | symbol is attached | subjected to the same member in the figure. The basic structure of the superconducting cable described in the embodiment is the same as the basic structure of the conventional superconducting cable described with reference to FIGS. 3 and 4, and the following description will focus on the differences from the conventional one. Description of this point is omitted.

[Embodiment 1]
FIG. 1 shows a cross section of the superconducting conductor layer of a cable core in a superconducting cable, cut in a direction perpendicular to the longitudinal direction. Actually, the superconducting conductor layer is formed by spirally winding a plurality of superconducting wires around the outer periphery of the former, and has a multilayer structure in which superconducting wires are laminated in the radial direction of the cable core. Of the layers of the superconducting conductor layer formed by the superconducting wire 120, only the inner peripheral layer 12a (first layer) closest to the former 11 is shown.

  In the superconducting conductor layer, the outer peripheral layer (second layer) is similarly formed on the outer periphery of the inner peripheral layer 12a by spirally winding the superconducting wire. A magnetic field smoothing layer 12m made of a magnetic material is provided between the outer peripheral side layers. The magnetic field smoothing layer 12m is formed substantially uniformly in the circumferential direction by, for example, winding a magnetic tape to be described later around the outer periphery of the inner peripheral layer 12a. The magnetic material constituting the magnetic field smoothing layer 12m is preferably a soft magnetic material having a relative magnetic permeability of 10 or more, such as pure iron, nickel, cobalt, silicon steel (eg, Fe-3 to 4% Si), permalloy ( Examples include Fe-35 to 85% Ni) and ferrite (eg, Mn-Zn ferrite, Ni-Zn ferrite). Here, the magnetic field smoothing layer 12m is made of nickel, for example.

  As a magnetic tape, the thing of the aspect shown in FIG. 2 is mentioned, for example. The magnetic tape M1 shown in FIG. 2 (A) is a magnetic tape made of only the magnetic material m. In addition, when the magnetic field smoothing layer 12m (see FIG. 1) is configured with the magnetic tape M1, if the interlayer insulation between the inner peripheral layer and the outer peripheral layer cannot be ensured, for example, the interlayer A combination of an interlayer insulating layer wound with paper and a magnetic field smoothing layer may be provided. If the size of the magnetic tape is about 20 mm wide and about 50-100 μm thick, it can be wound in the same way as the current interlayer paper.

  The magnetic tape M2 shown in FIG. 2 (B) is a magnetic tape in which the surface of the base material s is coated with a magnetic material m. As the substrate s, for example, kraft paper, composite paper in which kraft paper and plastic film are laminated (PPLP (registered trademark, Polypropylene Laminated Paper)), stainless steel, or the like can be used. As a method for coating the magnetic material m, for example, various physical vapor deposition methods such as vacuum vapor deposition and sputtering, chemical vapor deposition, or plating methods such as electrolytic plating and electroless plating can be used. In the magnetic tape M1, it is difficult to process the magnetic material m to a predetermined thickness of 2 μm or less, for example, but in the magnetic tape M2, the thickness of the magnetic material m is easily adjusted to a predetermined thickness. The size of the substrate is preferably about 20 mm in width and about 50 to 100 μm in thickness.

  When such a magnetic tape is wound to form a magnetic field smoothing layer on the outer periphery of the inner peripheral layer, the cross-sectional shape of the magnetic field smoothing layer changes depending on the properties of the magnetic tape. For example, when the magnetic tape is low in rigidity and easily deformed, the magnetic tape deforms corresponding to the outer shape of the inner peripheral layer when wound, so that the wire 120 is formed as shown in FIG. A cross-sectional shape of the magnetic field smoothing layer 12m is formed along the drawn outline. On the other hand, when the magnetic tape is highly rigid and has a certain degree of bendability, the magnetic tape can be wound into a circular shape irrespective of the outer shape of the inner peripheral layer, and as shown in FIG. In addition, the cross-sectional shape of the magnetic field smoothing layer 12m is formed in a circular shape. In the case of the magnetic tape M1, properties such as rigidity and bendability of the magnetic tape are determined by the magnetic material m to be configured. In the case of magnetic tape M2, it is determined by the combination and thickness of base material s and magnetic material m.For example, if a low-rigidity material such as kraft paper is selected as the base material, the rigidity of the magnetic tape will decrease, whereas the rigidity such as stainless steel If a material having a high thickness is selected, the rigidity of the magnetic tape is improved.

  The superconducting cable according to Embodiment 1 described above has the following effects. When a current flows through the superconducting conductor layer, the magnetic field smoothing layer suppresses the disturbance of the circumferential magnetic field generated by the inner circumferential layer, and the circumferential magnetic field is smoothed so as to approach a circle. The radial magnetic field applied to the outer peripheral layer is reduced, and the AC loss can be reduced. By configuring the magnetic field smoothing layer with a soft magnetic material having a relative magnetic permeability of 10 or more, the magnetic field can be easily passed through the magnetic field and smoothed, and the hysteresis loss in the magnetic field smoothing layer can be reduced. In particular, as shown in FIG. 1B, when the cross-sectional shape of the magnetic field smoothing layer is made closer to a circle, the circumferential magnetic field in the inner peripheral layer is smoothed so as to approach a more circular shape. AC loss can be reduced.

(Modification 1)
In this example, the thickness of the magnetic field smoothing layer is 2 μm or less. The thickness of the magnetic field smoothing layer may be appropriately determined according to the characteristics required for the magnetic field smoothing layer from the relationship with the magnetic properties such as the relative permeability and coercive force of the magnetic material. However, as the thickness of the magnetic field smoothing layer increases, the hysteresis loss tends to increase accordingly. Therefore, the hysteresis loss can be sufficiently suppressed by setting the thickness of the magnetic field smoothing layer to 2 μm or less. On the other hand, the lower limit value of the thickness of the magnetic field smoothing layer is preferably 0.5 μm in order to secure a magnetic path.

(Modification 2)
In this example, the superconducting wire is a RE123-based thin film wire. The superconducting wire may be either a silver sheath wire or a thin film wire, and is not particularly limited, but a thin film wire is preferably used. The thin film wire is excellent in loss characteristics with respect to the parallel magnetic field as compared with the silver sheath wire, and it can be expected that the effect of reducing the AC loss is increased. Further, by using a thin film wire, it is possible to reduce the thickness of the superconducting conductor layer, and to reduce the diameter of the cable core and thus the entire superconducting cable. Specific examples of the RE123-based thin film wire include a Y-based (YBCO) thin film wire and a Ho-based (HoBCO) thin film wire.

  In the case of the thin film wire, when spirally wound around the outer periphery of the former, either the superconducting thin film side of the thin film wire is directed to the radially inner peripheral side or the radially outer peripheral side of the cable core may be used. When facing the radially inner side, tensile stress is unlikely to act on the superconducting thin film, and the superconducting properties are less degraded. In the case of directing toward the outer peripheral side in the radial direction, electrical connection between the superconducting conductor layer and its connection object is easy at the intermediate connection portion or the terminal connection portion of the superconducting cable.

(Modification 3)
In this example, the relative permeability of the magnetic material is higher than the relative permeability of any material constituting the superconducting wire. In addition to the superconductor, a silver sheath or a stainless steel substrate is used as the superconducting wire. By making the relative permeability of the magnetic material higher than the material constituting these, it becomes easier for the magnetic field to pass through the magnetic field smoothing layer than the superconducting wire constituting the outer layer, and the effect of reducing AC loss by the magnetic field smoothing layer is greater. Can be expected. Examples of the magnetic material having a higher relative permeability than silver or stainless steel include the above-described soft magnetic materials such as nickel.

(Modification 4)
In the first embodiment described above, the example in which the magnetic tape is wound to form the magnetic field smoothing layer on the outer periphery of the inner peripheral layer has been described. Here, another method for forming the magnetic field smoothing layer will be described. . For example, the magnetic field smoothing layer can be formed by installing a cylindrical magnetic member made of a magnetic material on the outer periphery of the inner peripheral layer. The cylindrical magnetic member may be formed by combining a plurality of pieces of magnetic material into a cylindrical shape. In addition, the cylindrical magnetic member may be a cylindrical base material coated with a magnetic material, or a cylindrical base material formed by combining a plurality of divided base materials coated with a magnetic material. The cylindrical magnetic member is suitable when the cable length is short because a plurality of units need to be connected in series in the longitudinal direction.

  Note that the present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the gist of the present invention. In the first embodiment, the example in which the magnetic field smoothing layer is provided between the first layer and the second layer of the superconducting conductor layer has been described. For example, when the superconducting conductor layer has a multilayer structure of three or more layers, If a magnetic field smoothing layer is provided in any of the layers, the AC loss reduction effect according to the present invention can be obtained. Further, if a magnetic field smoothing layer is provided in all layers, the effect of reducing AC loss is great.

  The superconducting cable of the present invention can be suitably used in the field of AC superconducting power transmission.

100 superconducting cable
10 Cable core
11 Former 12 Superconducting conductor layer 13 Insulating layer
14 Superconducting shield layer 15 Normal conducting protective layer
20 Insulated pipe
21 Inner pipe 22 Outer pipe 23 Insulation 24 Anticorrosion layer
120 Superconducting wire
12a Inner layer 12b Outer layer
12i Interlayer insulation layer 12m Magnetic field smoothing layer
g gap
M1, M2 Magnetic tape m Magnetic material s Base material

Claims (6)

A superconducting cable comprising a cable core having a superconducting conductor layer formed by spirally winding a plurality of superconducting wires around the former,
The superconducting conductor layer has a multilayer structure in which superconducting wires are laminated in the radial direction of the cable core,
In the superconducting conductor layer, a magnetic field smoothing layer made of a magnetic material is provided between an inner peripheral layer and an outer peripheral layer.   The superconducting cable according to claim 1, wherein the magnetic material has a relative permeability of 10 or more.   The superconducting cable according to claim 1, wherein the magnetic material is a soft magnetic material.   The superconducting cable according to any one of claims 1 to 3, wherein a relative permeability of the magnetic material is higher than a relative permeability of any material constituting the superconducting wire.   The thickness of the said magnetic field smoothing layer is 0.5 micrometer or more and 2 micrometers or less, The superconducting cable as described in any one of Claims 1-4 characterized by the above-mentioned.   The superconducting cable according to any one of claims 1 to 5, wherein the superconducting wire is a thin film wire.

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